I adore the style, but I have to agree with the other comments on the hijacking mechanic - it feels very rough to grind through several encounters to build my SP up, then actually run into a Sleeper rather than a fairy or kedama, then carefully lower their HP a bit so the pattern is easier, and only then take a shot at the minigame (and if I mess up, it's back to square one).
Also, there's a bug where you can use the SP-based buffs even if you don't have enough SP.
Maybe there could be a "force an encounter" button to spare the player from having to walk back and forth?
Looking forward to more!